Positive feedback between future climate change and the carbon cycle

Future climate change due to increased atmospheric CO₂ may affect land and ocean efficiency to absorb atmospheric CO₂. Here, using climate and carbon three-dimensional models forced by a 1% per year increase in atmospheric CO₂, we show that there is a positive feedback between the climate system and the carbon cycle. Climate change reduces land and ocean uptake of CO₂, respectively by 54% and 35% at 4 × CO₂ . This negative impact implies that for prescribed anthropogenic CO₂ emissions, the atmospheric CO₂ would he higher than the level reached if climate change does not affect the carbon cycle. We estimate the gain of this climate-carbon cycle feedback to be 10% at 2 × CO₂ and 20% at 4 × CO₂ . This translates into a 15% higher mean temperature increase.